Blender Model Resizing after being Parented to Rig
I know you would prefer a better solution, but: I know that .stl import has an option to use scene units, and it works for that format, helps sometimes to solve problems like this. 

So maybe you could try to import the .obj, export in .stl, and then import the .stl using that option (or not, depending if any of the two fits). 

Works since 2.73, afaik.